1. Field of the Invention
The present invention relates to nanometer scale electronic devices. More particularly, this invention pertains to nanoscale switches and to devices for measuring the electrical characteristics of conjugated molecular wires.
2. Description of the Prior Art
The emerging field of nanotechnology and nanometer-scale devices offers the promise of molecular digital logic circuits that are on the order of one million times smaller than the corresponding conventional silicon semiconductor logic circuits. (Note: xe2x80x9cnanometer scalexe2x80x9d ranges from approximately 0.1 to 50 nanometers in contrast to the sub-micron scale range of approximately 50 nanometers (0.05 micrometers) to one micrometer and the micron scale range of approximately one to a few micrometers, each of which is commonly encountered in silicon device technology.)
Nanometer-scale devices are based upon molecular building blocks having well-understood electrical properties. Such molecular building blocks are arranged to operate analogously to micron scale or submicron scale electronic devices.
The very small scale of nanoscale devices introduces, or enhances the importance of certain fabrication issues, such as the creation of nanoscale gaps between metallic electrodes.
One of the primary circuit elements of digital logic and systems is the three terminal voltage-controlled switch in which a flow of current between a pair of electrodes is regulated by the application of a gating voltage at a third device electrode. Unfortunately, this essential step in the development of nanoscale systems has been hampered by known physical limitations associated with the very small size desired. Such limitations have complicated the search for a nanoscale analog to the field effect transistor (xe2x80x9cFETxe2x80x9d).
In a traditional micron-scale FET formed in silicon, a gate electrode is provided for applying a voltage that regulates the conductance of a channel sandwiched between source and drain electrodes. For example, the interaction of the gate voltage with the material of the channel regulates the size of a depletion region devoid of majority carriers (holes or electrons) and strongly affects the conducting channel. This phenomenon and mode of operation, whereby the resultant source-to-drain current flow is regulated by the switching effect of a gating voltage, is well understood in the art.
The above-described manner of operation of a FET cannot be obtained when the device is reduced to nanometer scale (e.g., channel length less than 15 nm) since, with such a small channel length, the separation between source and drain electrodes is too small to allow the gate voltage to predominately control the carrier density. Current is controlled by injection from the source electrode.
FIG. 1 shows a prior art FET having a source electrode 14 and a drain electrode 16, each of highly-doped silicon, formed on a dielectric layer 18 that, in turn, is formed on top of a highly doped substrate 20 that serves as gate electrode. A spin-coated thin layer 22 of organic material, about 300 Angstroms (=30 nm) thick, lies between the source and drain electrodes 14 and 16 and serves as the channel region of the FET 10. Application of a voltage to the gate electrode controls conductance through the organic layer 22 between the source and drain electrodes.
The channel comprises the organic layer 22, but the remainder of the FET 10 comprises a standard silicon technology layout with the conductance between source and drain electrodes controlled by the response of the organic layer 22 to the applied gate voltage.
A relatively high gate voltage (30 to 50 V), a function of the thickness of the dielectric layer 18, is required to change the conductance of the layer 22 of organic material. Since the conductance and mobility of an organic layer are relatively low (i.e., less than 1 cm2/(V-s), an often-unacceptably slow switching speed and low drain current are obtained.
The preceding and other shortcomings of the prior art are addressed by the present invention that provides, in a first aspect, a nanoscale switch. Such switch includes a conductive substrate. A dielectric layer overlies the conductive substrate.
A first electrode and a second electrode are located on the dielectric layer in spaced relation separated from one another by a gap. A first electrically conductive molecular wire and a second electrically conductive molecular wire are provided.
The first molecular wire is bound to the first electrode and to an electrically conductive nanoparticle and the second molecular wire is bound to the second electrode and to the nanoparticle whereby an electrically conductive path exists between the first and second electrodes.
In a second aspect, the invention provides apparatus for measuring the electrical characteristics of conductive molecular wires. Such method is begun by providing a layer of dielectric material. A first electrode and a second electrode are formed on the dielectric layer with a gap therebetween.
A first plurality of electrically-conductive molecular wires is bonded to the first electrode and a second plurality of molecular wires is bonded to the second electrode. The electrical conductivity of the nanoparticle exceeds that of the first and said second molecular wires. An electrically-conductive nanoparticle is then bonded to at least one molecular wire of the first plurality of molecular wires and to at least one molecular wire of the second plurality of molecular wires.
A voltage difference is then created between the first and second electrodes and a resultant flow of electrical current between the first and second electrodes through the molecular wires and nanoparticle is measured.
In a third aspect, the invention provides apparatus for measuring electrical characteristics of conductive molecular wires. Such apparatus includes a layer of dielectric material. A first electrode and a second electrode are located on the layer of dielectric material in spaced relation separated from one another by a gap.
First and second electrically conductive molecular wires are provided. The first molecular wire is bound to the first electrode and to a conductive nanoparticle and the second molecular wire is bound to the second electrode and to the nanoparticle whereby an electrically conductive path exists between the first and second electrodes.
Means are provided for establishing a voltage difference between said first and second electrodes as well as means for measuring the flow of current between the first and second electrodes through the electrically conductive path in response to such voltage difference between the first and second electrodes.
The preceding and other features of the present invention will become clear from the detailed description that follows. Such description is accompanied by a set of drawing figures. Numerals of the drawing figures, corresponding to those of the written description, point to the features of the invention. Like numerals refer to like features throughout both the written description and the drawing figures.